Mitering gauges are attached to woodworking machines for making angled joints between two work pieces. Typically, the joints are formed by cutting the ends of the two work pieces at equal angles. Each of the two ends of the work pieces are separately oriented with respect to a cutting tool at a predetermined angle that is set by the mitering gauge.
For example, it is well known to use a mitering gauge as an attachment to a table saw for orienting a work piece with respect to a rotating saw blade. One edge of the work piece is held against a straightedge or "fence" that is oriented at a predetermined angle with respect to the saw blade. The fence is moved with respect to the saw blade for feeding the work piece into engagement with the saw blade. Different angles may be cut in the ends of wood pieces by angularly adjusting the fence with respect to the direction of the feed movement.
One widely used type of mitering gauge features a fence which is pivotally mounted on a guide rail that slides within a groove (also referred to as a miter slot) formed in a saw table top. The miter slot is parallel to the plane of rotation of the saw blade. One side of the fence functions as a straightedge for aligning a surface or edge of a work piece and the other side supports a gauge that is graduated with a protractor scale. The gauge pivots together with the fence past a reading mark on the guide rail for orienting the fence to a predetermined angle. A thumb screw or similar means tightens the gauge to the guide rail. The work piece is mounted so that one end extends beyond the length of the fence, and the work piece together with the mitering gauge is guided along the miter slot formed in the table top to cut off the end of the work piece at the desired angle with the saw blade.
Although it is possible to set this type of widely used gauge within a tolerance of less than one degree, errors of a magnitude no greater than five minutes may be noticeable in four inch length miter joints. Accordingly, several "trial and error" cuts may be required to set the gauge at an angle that will produce an accurate joint. Such trial and error cuts are time consuming and wasteful of work piece material.
Some of these known mitering gauges also include locating pins for more conveniently setting the gauges to a limited number of widely used angles. The locating pins are attached to the guide rails and are sized to engage one of a number of bores formed in an arcuate peripheral portion of the gauges. The bores are spaced at predetermined angles about the peripheral portion and are aligned with the locating pin by pivoting the gauge to one of the predetermined angles.
The locating pins provide for some improvement in the accuracy and repeatability of the known mitering gauges at a limited number of selected angles; but the gauges are difficult to manufacture, assemble, and maintain within a tolerance that avoids noticeable errors in miter joints. Much of this difficulty is related to a very limited radial distance that separates the fence pivot from the bores in the arcuate portion of the gauge. Even slight errors in the spacing or sizing of the bores lead to considerable angular errors in the orientation of the fence.
Another known type of mitering gauge features a sliding plate for supporting a work piece and for feeding the work piece into a rotating blade. The plate is rectangularly shaped and is sized to cover a portion of a saw table top on one side of the saw blade. A guide rail is attached to the bottom of the plate for sliding within a miter slot formed in the saw table top. One end of an extended length fence is pivotally mounted on a top surface of the plate near the blade for orienting work pieces with respect to the guide rail. A graduated scale is located along a far edge of the plate which can be read against the other end of the fence for orienting the fence to a desired angle. A fastener carried by the fence engages an arcuate slot in the plate centered at the fence pivot for locking the fence to the plate at the desired angle.
Although the scale along the far edge of the plate is located at a substantial distance from the pivot axis, contributing to greater accuracy, considerable skill and experience with the gauge are required to set the gauge within a tolerance that avoids noticeable errors. In addition, a correct setting is not easily repeatable once the gauge has been moved to another position.
Yet another known type of mitering gauge is disclosed in U.S. Pat. No. 3,841,188 to Wiater. The gauge is mounted directly on a saw table top, and a saw blade performs a feed movement within a slot formed through the table top. A fence is divided into two sections by a pivot axis. One section of the fence is mounted on the table top at a fixed angular orientation to the blade slot but may be adjusted through a short distance along the slot. The other section of fence is adjusted angularly about the pivot axis for orienting a work piece with respect to the blade slot. A thumb screw carried by the angularly adjustable fence section engages one of a number of holes tapped in the table top for setting the fence at a fixed angular orientation. Since the one fence section can be adjusted along the slot, the angularly adjustable fence section can be set through a continuum of angles even though only a limited number of tapped holes are provided for maintaining the angularly adjustable fence section in a fixed orientation. However, the ability to adjust the one fence section along the slot requires that trial and error efforts be used to set the angularly adjustable fence section to a desired angle.